| Background Since 1986 the concept of ischemic preconditioning was proposed by Murry, several strategies (such as low temperature, electro-acupuncture, etc.) as well as drugs (such as excitatory amino acid antagonists, free radical scavengers, minocycline, etc.) have been proved to induce ischemic tolerance in the organs. However, most observation time of these studies'did not exceed 72 hours after reperfusion. It was suspected that preconditioning didn't permanently prevent cell death after ischemic/reperfusion injury, but only postponed the evolution of the progress of cell death. Whether the protective effects will gradually weaken, disappear or not change in a long-term observation is a question disputable but very important that need us to answer. Our previous study showed that hyperbaric oxygen (hyperbaric oxygen, HBO) preconditioning can simulate "ischemic preconditioning" and induce ischemic tolerance in spinal cord ischemic/reperfusion injury. This phenomenon also exists in focal cerebral ischemia model of rats. Another study showed that apoptosis does exist in ischemia/reperfusion injury in the central nervous system, and the delayed cell injury of ischemia/reperfusion in spinal cord is mainly caused by apoptosis rather than necrosis. Hyperbaric oxygen preconditioning can reduce early apoptosis of neurons and may even reverse apoptosis. Therefore, this study take "the ischemic tolerance induced by hyperbaric oxygen preconditioning in rabbit spinal cord" as the breakthrough point, to study the neuroprotective effect of HBO preconditioning for long-term observation and the relationship between the long-term effects and neuron apoptosis.Partâ… Long-standing ischemic tolerance induced by hyperbaric oxygen preconditioning in spinal cord of rabbitsObjective To determine if the ischemic tolerance induced by hyperbaric oxygen preconditioning in spinal cord of rabbits is long-standing. Methods In experiment 1, sixteen male New Zealand rabbits were randomly assigned to 2 groups (8 in each group) : animals in control group received room air and normal ambient pressure (1 h/d, 5 d); animals in HBO group received HBO pretreatment (100% O2, 2.5 atmosphere absolute [ATA], 1 h/d, 5 d). At 24 hours after the last treatment, the spinal cord ischemia was induced for 20 min by infrarenal aortic cross clamping. At 1day, and 2, 7, 14, 21 days after reperfusion, the neurologic function was scored by the Tarlov criteria (in which 4 was normal and 0 was paraplegia). In experiment 2, thirty-two animals were also randomly assigned to HBO group and control group (16 in each group). Animals underwent the same treatment as in experiment 1. Then eight animals in each group were sacrificed at 2 days and 21 days after reperfusion, respectively. And their spinal cords (L5-7) were removed immediately for histopathologic examination. The neurologic functions were scored before they were sacrificed.Results The neurologic function scores in HBO group were significantly greater than in control group at all time points (P<0.05), which had no statistical differences between 7,14 or 21 days and 2days in HBO group (P>0.05). The numbers of normal neurons in the anterior spinal cord in HBO groups were also significantly greater than in control groups at 2 days and 21 days, which had no statistical differences between 2 days and 21 days in HBO groups. There was a strong correlation between the neurologic function scores and the numbers of normal neurons in the anterior horn of the spinal cords (r2d =0.903, P<0.01; r21d =0.922, P<0.01). Conclusion Hyperbaric oxygen preconditioning induced ischemic tolerance in spinal cord of rabbits and the effect is long-standing.Partâ…¡The relationship between the long-standing ischemic tolerance induced by hyperbaric oxygen preconditioning and the cell apoptosis after reperfusion in spinal cord of rabbitsExperiment 1 The relationship between the long-standing ischemic tolerance induced by hyperbaric oxygen preconditioning and the early stage apoptosis after reperfusion in spinal cord of rabbitsObjective To determine if hyperbaric oxygen preconditioning induced long-standing ischemic tolerance via reducing the early stage apoptosis after reperfusion in spinal cord of rabbits. Methods Fifty male New Zealand rabbits were randomly assigned to 2 groups (25 in each group) : animals in control group received room air and normal ambient pressure (1 h/d, 5 d); animals in HBO group received HBO pretreatment (100% O2, 2.5 ATA, 1 h/d, 5 d). At 24 hours after the last treatment, the spinal cord ischemia was induced for 20 min by infrarenal aortic cross clamping. Five animals in each group were sacrificed at 8, 24 hours and 2, 3, 5 days after reperfusion, respectively. And their spinal cords (L5-7) were removed immediately for TUNEL staining. The neurologic functions were scored before they were sacrificed. Results The neurologic function scores in HBO groups were significantly less than that in control groups at 24 hours and 2, 3, 5 days after reperfusion(P<0.05), which had no statistical differences at 8 hours (P>0.05). The numbers of TUNEL positive neurons in HBO groups were significantly less than that in control groups at all time points(P<0.05). Conclusion Hyperbaric oxygen preconditioning induced long-standing ischemic tolerance via reducing early stage apoptosis after reperfusion in spinal cord of rabbits.Experiment 2 The relationship between the long-standing ischemic tolerance induced by hyperbaric oxygen preconditioning and the later stage apoptosis after reperfusion in spinal cord of rabbitsObjective To determine if hyperbaric oxygen preconditioning induced long-standing ischemic tolerance via reducing the later stage apoptosis after reperfusion in spinal cord of rabbits. Methods Forty male New Zealand rabbits were randomly assigned to 2 groups (20 in each group) : animals in control group received room air and normal ambient pressure (1 h/d, 5 d); animals in HBO group received HBO pretreatment (100% O2, 2.5 ATA, 1 h/d, 5 d). At 24 hours after the last treatment, the spinal cord ischemia was induced for 20 min by infrarenal aortic cross clamping. Five animals in each group were sacrificed at 2, 7, 14, 21 days after reperfusion, respectively. And their spinal cords (L5-7) were removed immediately for TUNEL staining and FJ-B staining. The neurologic functions were scored before they were sacrificed. Results Neurologic function scores in HBO groups were significantly greater than that in control groups at all time points (P<0.05). The numbers of TUNEL positive neurons in HBO groups were significantly less than in control groups at 2 and 7 days(P<0.05), and FJ-B positive neurons in the anterior spinal cord in HBO groups was only significantly less than that in control group at 2 days(P<0.05), which had no statistical differences at other time points(P>0.05). Conclusion The long-standing ischemic tolerance induced by hyperbaric oxygen preconditioning doesn't significantly related to later stage apoptosis after reperfusion in spinal cord of rabbits.
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